N-confused Porphyrin Research Articles

Ruthenium N-Confused Porphyrins: Selective Reactivity for Ambident 2-Heteroatom-Substituted Pyridines Serving as Axial Ligands.

Three types of ruthenium(II) N-confused porphyrin (NCP) complexes bearing an axial 2-thiopyridine, 2-pyridone, and 2-iminopyridine moiety at the inner carbon atom, respectively, were synthesized. The unique reactivity of the 2-substituted pyridine derivatives (2-X-pyridine; X=SH, OH, NH2 ) toward the inner carbon atom of the NCP allows the formation of two types of coordinated products (i. e., pyridine donor versus 2-heteroatom donors), as inferred from single-crystal X-ray structures. The selective reactivity was investigated by using density functional theory (DFT) calculations. Finally, the catalytic activity of these ruthenium complexes was demonstrated through the styrene oxidation reactions. As a result, the ruthenium(II) NCP complex bearing a 2-thiopyridine moiety, together with aqueous H2 O2 as an oxidant showed the highest selectivity for benzaldehyde (benzaldehyde/styrene oxide=20 : 1).

N-Confused Porphyrin-aza-Dipyrrin Chimera: A Versatile Metal Coordination Ligand Using its Unique NH Tautomerism.

A novel N-confused porphyrin (NCP) analogue bearing an external aza-dipyrrin-like coordination site was synthesized by a Schiff-base forming reaction of N-confused oxoporphyrin and 2-aminopyridine derivatives. The chimera molecule enhances the intrinsic NH tautomerism of NCP to enable four possible tautomeric structures, three of which were identified by metal coordination.

Reactions of 2-aza-21-carbaporphyrin with aniline derivatives

Post-synthetic modification of N-confused porphyrin (NCP) yields chiral 21-arylazo- or 3,21-bis(arylamino)-NCP in one-step, one-pot reactions of NCP with anilines.

Zinc 2-N-methyl N-confused porphyrin: an efficient catalyst for the conversion of CO2 into cyclic carbonates

A zinc 2-N-methyl N-confused porphyrin (Zn(NCP)Cl) catalyst was developed for the solvent-free synthesis of cyclic carbonates from epoxides and CO2.

Ni and Pd N-confused porphyrin complexes as catalysts for the synthesis of cyclic carbonates from epoxides and CO2.

We have demonstrated the design of a novel bifunctional catalyst that is based on an N-confused tetraphenylporphyrin (NCTPP) motif for the cycloaddition of an epoxide to carbon dioxide via cooperative activation of the epoxide through a Pd(ii) or Ni(ii) metal center and a peripheral benzoate moiety with percent conversions of up to 99% and TON = 7000.

The selectivity between inner C-cyanation and alkylation in cobalt(II) complexes of N-confused porphyrin with an axial NCS− ligand

Some inner C-cyanation and C-alkylation complexes have been described. Reactions of 2-N-substituted N-confused tetraphenylporphyrin (2-NCH2YNCTPPH) with Co(SCN)2 afford C-alkylation (14) and C-cyanation (15–17) complexes. The crystal structures for the inner C-alkylation product of thiocyanato(2-aza-2-[p-methylbenzyl]-5,10,15,20-tetraphenyl-21-benzyl-21-carbaporphyrinato-N,N′,N″)cobalt(II)·0.5 octane solvate [Co(2-NCH2-p-CH3C6H4-21-CH2C6H5NCTPP)(NCS)·0.5C8H18; 14·0.5C8H18] and the inner C-cyanation products of thiocyanato(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II) [Co(2-NCH2COOCH2CH3-21-CN NCTPP) (NCS); 15], thiocyanato(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II)[Co(2-NCH3-21-CNNCTPP) (NCS); 16], and thiocyanato(2-aza-2-benzyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II) [Co(2-NCH2C6H5-21-CNNCTPP) (NCS); 17] have been reported. The geometry around Co2+ ion in these four complexes is a distorted tetrahedron with a C2v symmetry. Two possible mechanisms were proposed to explain the formation of inner C-alkylation (14·0.5C8H18) versus C-cyanation (15–17) products in these complexes with an axial *NCS− ligand.

Electrochemistry of N-confused inner amino-substituted free-base tetraarylporphyrins in nonaqueous media

Four N-confused free-base tetraarylporphyrins containing an amino group on the inner carbon of the inverted pyrrole were synthesized and characterized as to their electrochemical and spectroelectrochemical properties in dichloromethane and N,N-dimethylformamide containing 0.1 M tetra-[Formula: see text]-butylammonium perchlorate as supporting electrolyte. The examined compounds are represented as (NH[Formula: see text](Ar)[Formula: see text]NcpH[Formula: see text], where “Ncp” is the N-confused porphyrin macrocycle and Ar is a [Formula: see text]-CH[Formula: see text]OPh, [Formula: see text]-CH[Formula: see text]Ph, Ph or [Formula: see text]-ClPh substituent on each meso-position of the macrocycle. Each porphyrin undergoes multiple irreversible reductions and oxidations. The first one-electron addition and first one-electron abstraction are located on the porphyrin [Formula: see text]-ring system to give [Formula: see text]-anion and [Formula: see text]-cation radicals with a HOMO–LUMO gap ranging from 1.21 to 1.34 V in CH[Formula: see text]Cl[Formula: see text] and 1.06 to 1.12 V in DMF. Both electrogenerated products are unstable and undergo a rapid chemical reaction to give new electroactive species which can be further reduced at more negative potentials or further oxidized at more positive potentials. The effects of the inner amino-substituent on the UV-vis spectra and electrochemical properties of the porphyrin are discussed, and comparisons made to data in the literature for both structurally related N-confused porphyrins containing an inner carbon NO[Formula: see text] group and derivatives without the inner substituent.

Syntheses and Redox Chemistry of Antiaromatic Core-Modified Isophlorinoids

During the attempted total synthesis of chlorophyll, Woodward hypothesized the formation of tetrapyrrolic 20π isophlorin as a transient antiaromatic intermediate which provides a plausible template to synthesize stable antiaromatic molecules. Despite its structural similarity with the 18π aromatic porphyrin, it significantly differs in its electronic and chemical properties. However, due to its unstable nature under ambient conditions it immediately gets oxidized to stable 18π aromatic porphyrin. Similar macrocyclic structures with β-substituted heterocycles, such as furan/thiophene/selenophene, have been synthesized, which undergo facile oxidation to yield the 18π porphyrin dication. Attempts to synthesize stable tetrapyrrolic isophlorin and its metal complex have remained unaccomplished till date. Strategies to synthesize stable core-modified 20π isophlorin and its confused isophlorin derivative have met with considerable success. Predominantly, they are synthesized by replacing three or four pyrroles with furan/thiophene. The 20π systems either with four furan units or with a ‘pair’ of furan and thiophene units were sufficiently stable enough to resist oxidation towards the corresponding porphyrin dication. The 20π isophlorins displayed noncovalent interactions with the curved π surface of fullerene which predominantly rises due to van der Waals attraction between the dissimilar π systems. This antiaromatic isophlorin-fullerene complexes were obtained and successfully characterized by single-crystal X-ray diffraction studies. Replacing only three pyrroles by furan rings yielded the first stable pyrrole derivative of antiaromatic 20π isophlorin, which can be reversibly oxidized to 18π aromatic porphyrin without deprotonating the inner pyrrole NH. In addition, replacing all the pyrrole units of N-confused porphyrin with thiophene yielded the first derivative of confused isophlorin. Further, its two-electron oxidation led to the formation of 18π aromatic cation with enhanced aromaticity. The structure and electronic properties of the oxidized and neutral species were unambiguously determined from a combination of spectroscopic techniques, X-ray crystallography, and computational methods. These studies reveal that antiaromatic systems like isophlorin and its confused isophlorin derivative can be stabilized under ambient conditions and they offer potential to explore the chemistry of 4nπ systems. This Account focuses of recent advances in 20π antiaromatic isophlorins, confused isophlorins, and nocorroles along with their redox chemistry. 1 Introduction2 Stable 20π Isophlorins2.1 Furan-/Thiophene-Based Isophlorins2.2 Pyrrole Isophlorins3 Confused Isophlorins3.1 Isophlorin-Fullerene3.2 meso-meso-Bridged Tetraoxaisophlorin Dimer4. Norcorroles5. Conclusion and Outlook

N-Confused Porphyrin Immobilized on Solid Supports: Synthesis and Metal Ions Sensing Efficacy.

In this work, the N-confused porphyrin 5,10,15,20-tetraphenyl-2-aza-21-carbaporphyrin (NCTPP) was immobilized on neutral or cationic supports based on silica and on Merrifield resin. The new materials were characterized by appropriate techniques (UV-Vis spectroscopy, SEM, and zeta potential analysis). Piezoelectric quartz crystal gold electrodes were coated with the different hybrids and their ability to interact with heavy metals was evaluated. The preliminary results obtained showed that the new materials can be explored for metal cations detection and the modification of the material surface is a key factor in tuning the metal selectivity.

N‐Confused Porphyrin Metal Complexes with an Axial Pyridine Directly Tethered from an Inner Carbon: A Bioinspired Ligand as a Versatile Platform for Catalysis

Bioinspired pentadentate ligand N‐confused porphyrin (NCP) bearing a 2‐mercaptopyridine group and its RuII and CoIII complexes were synthesized. Their structures were revealed by single‐crystal X‐ray crystallographic analysis. Installation of an axial thiopyridine ligand shifts the redox potentials negatively and enhances the catalytic activity largely, which was demonstrated in the cyclopropanation reaction using the Co complex.

Photophysical properties of free-base and manganese(iii) N-confused porphyrins.

The photophysical properties of N-confused 5,10,15,20-tetraphenyl porphyrin derivatives have been studied using steady-state and time-resolved spectroscopic techniques. The peripherally substituted N-confused 5,10,15,20-tetraphenyl free-base porphyrins (NCTPPs) show stronger B-band absorptions in DCM than in DMAc, while much stronger emissions have been observed in DMAc, which may be due to the shorter times (τIC) of internal conversion from the B-band to the Q-band. The Q-band spectral structures of NCTPPs in DCM are significantly different from those in DMAc. The introduction of ortho-OCH3 results in the strongest emission in both DCM and DMAc and significant fluorescence after N-methylation even though the emissions of other N-methyl complexes are quenched. The N-methylation of NCTPPs leads to a larger τIC and shorter emission lifetime. The excited-state dynamics of manganese(iii) N-confused porphyrins (Mn(Cl)NCH3NCTPPs) are influenced by both peripheral substituents and manganese(iii) metal ion, and exhibit ultrafast intersystem crossing processes.

The η1-H-CHg agostic interactions in the mercury complexes of N-confused porphyrin.

Six four-coordinated complexes of the chemical formulae [Hg(2-N CH2COOCH2CH3-21-H-NCTPP)X] with X = Cl (5), Br (6), I (7), [Hg(2-NCH3-21-H-NCTPP)Cl] (4) and [Hg(2-NCH2COOCH2C6H5-21-H-NCTPP)X] with X = Cl (8), I (9) are synthesized and structurally determined. The bond path for the weak η1-H(17)-C(17)Hg agostic interactions between the Hg center and H(17) in complexes 4-9 was a through-space interaction from Hg to agostic carbon [C(17)] followed by a through-bond interaction from C(17) to an agostic proton [H(17)]. The magnitude of J[Hg-H(17)] [or the agostic upfield shift Δδago of the C(17)] for these complexes increases as the halide ligand varies from iodide to chloride, ranging from 33.2 Hz (or 14.3 ppm) for I- to 36 Hz (or 15.8 ppm) for Br- and 36.9 Hz (or 16.0 ppm) for Cl-. The plot of J[Hg-H(17)] for the agostic proton H(17) versus |Δδago| for the agostic carbon atom C(17) in compounds 3-9 was linearly expressed as J[Hg-H(17)] = 2.29 |Δδago| + 0.13.

Synthesis of 3-Cyano-21-Nitro-N-Confused Porphyrin Derivatives by Isoamyl Nitrite

The 3-cyano-21-nitro- N-confused porphyrin derivatives were synthesised by the nitration reaction of 3-cyano- N-confused-porphyrin with isoamyl nitrite at room temperature in moderate yield. The reaction took placed regioselectively in 21-position carbon of inverted pyrrole of N-confused porphyrins.

Tautomerism-Induced Cis-Trans Isomerization of Pyridylethenyl N-Confused Porphyrin.

Pyridylethenyl-substituted N-confused porphyrins (NCPs) were synthesized, and their cis-trans isomerization was studied. Among four possible isomers, trans-3H and cis-2H types of structures, of which aromaticity and absorption/emission properties differ largely, were isolated. The cis-isomer was largely stabilized by the intramolecular hydrogen bonding between the pyrrolic-NH and the pyridinic-N in the vicinity. The thermal cis-trans isomerization proceeded even at 30 °C, which was significantly accelerated by the pyridine added to the system. The kinetic studies revealed that the isomerization reaction was second-order and the activation energy of the thermal isomerization from cis to trans isomer was ΔG0⧧cis→trans = 35.7 kcal/mol at 298 K, which is significantly smaller than that of Ni complex (42.3 kcal/mol). An intermolecular proton transfer induced cis-trans isomerization mechanism was proposed.

Organometallic Group 11 (CuIII , AgIII , AuIII ) Complexes of a trans-Doubly N-Confused Porphyrin: An "Expanded Imidazole" Structural Motif.

Complexation of group 11 metal cations with an α-bis(phenylthio)-substituted trans-doubly N-confused porphyrin (trans-N2 CPSPh : 4) afforded a series of square-planar trivalent organometallic complexes (i.e., Cu-H4, Ag-H4, and Au-H4). The X-ray crystal structures of the complexes revealed highly planar core geometries along with the presence of peripheral amine and imine nitrogen sites of the pyrrolic moieties. NMR, UV/Vis absorption, and magnetic circular dichroism (MCD) spectroscopies suggested the 18 π-electron aromaticity of the complexes. The aromaticity was also fully analyzed by various theoretical methodologies such as nucleus-independent chemical shift (NICS) and anisotropic induced current density (ACID) calculations. The central metal affects the amphiprotic character of the complexes possessing both pyrrolic amino nitrogen and imino nitrogen atoms at the periphery, which was examined by the photometric titration with trifluoroacetic acid (TFA) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), respectively. The inherent acidity of the complexes was followed in the order; Cu-H4>Au-H4>Ag-H4 and that of basicity was Au-H4>Ag-H4>Cu-H4. The complexes could be considered as an "expanded imidazole" structural motif.

Synthesis of 3-cyano-N-confused porphyrin derivatives by silyl cyanide

3-Cyano- N-confused porphyrin derivatives were synthesised by the reaction of N-confused porphyrin with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride in moderate yield. The reaction took placed regioselectively in the 3-position carbon of the inverted pyrrole of N-confused porphyrins.

Zirconium-based Metal–Organic Frameworks with N-Confused Porphyrins: Synthesis, Structures, and Optical Properties

Abstract Metal–organic frameworks (MOFs) composed of zirconium (Zr6) and N-confused porphyrins (NCPs) were synthesized. The cubic structures with ftw topology were determined by powder X-ray diffraction and microscopic analyses. These complexes represent high chemical stability toward various pH ranges and NIR absorption/emission derived from the NCP moieties.

Magnetic Circular Dichroism of Transition-Metal Complexes of Perfluorophenyl-N-Confused Porphyrins: Inverting Electronic Structure through a Proton.

Neutral and deprotonated anionic Ni(II), Pd(II), Cu(II), and Cu(III) complexes of tetrakis(perfluorophenyl)-N-confused porphyrin (PF-NCP) were prepared and investigated by UV-visible and magnetic circular dichroism (MCD) spectroscopies. As in the previously reported Ni(II) adduct of tetraphenyl N-confused porphyrin, we observe sign reverse (positive to negative intensities with increasing energy) features in the MCD spectra of the neutral Ni(II), Pd(II), and Cu(II) complexes of PF-NCP, which is indicative of rare ΔHOMO < ΔLUMO relationships. Upon deprotonation of Ni(II), Pd(II), and Cu(II) complexes, these features revert to those of more typical porphyrin MCD spectra consistent with a ΔHOMO > ΔLUMO condition. The Cu(III) PF-NCP complex shows features similar to those of the deprotonated divalent metal systems. Spectroscopic features in all target complexes as well as previously published metal-free and Ni(II) NCP systems were correlated with the density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. Calculation data are consistent with the tautomeric rearrangement of the electronic structures of NCP cores playing dominant roles, with smaller contribution from the central metal ions in the observed optical and magneto-optical properties. This is true for all described NCP systems to date, as they affect the stabilization/destabilization of the N-confused porphyrin-centered Gouterman orbitals.

Hydrogen Generation Catalyzed By Metalloporphyrins

Hydrogen has potential of being used as the future green fuel in fuel cells. The demand and consumption of hydrogen have predicted to continuously rise in the next two decades. Nevertheless, a highly efficient and low cost of water-splitting catalyst for hydrogen generation remains elusive. In this presentation, we synthesize a series of metalloporphyrin complexes in order to elucidate the effects of porphyrinic structure to the catalytic efficiencies. It is found that the metalloporphyrins with different substituents demonstrated different catalytic activities. A porphyrin with acidic substituents appears to be essential to offer high catalytic efficiencies. Additionally, a substituent located closer to the metal ion center will be better than oriented outward in respect to the central core. Our results also suggest that the type of central metal ions is another factor that control the activity of the hydrogen generation catalysts. Through the comparison on the CV of two novel N-confused porphyrin cobalt nitrosyl complexes, it appears that the activities of the catalysts depend on the reduction sites where the reducing equivalent will reside, i.e. a Co(NO) moiety based reduction has a more positive onset potential than a porphyrin-based reduction.

Charged and confused: Meso-tetrakis(p-methoxycarbonyl-phenyl) N-confused porphyrin as a precursor to water soluble variants

A metal-free meso-tetrakis([Formula: see text]-methoxycarbonylphenyl) N-confused porphyrin (1) was prepared as the precursor for water-soluble derivatives by the reaction between pyrrole, methyl-4-formylbenzoate, and MSA. Tautomeric behavior of the porphyrin 1 in polar and non-polar solvents was probed by [Formula: see text]H NMR, UV-vis, MCD, steady-state fluorescence, and high-resolution ESI methods and was found to be similar to the previously reported metal-free N-confused porphyrins. The electronic structure and the nature of the excited states in 1 were correlated with the results obtained by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.